576 Chapter 13:Quality Control
(d) Ifμis increased by 60, what is the probability of a subgroup average falling
outside the control limits?
10.The following data refer to the amounts by which the diameters of^14 -inch ball
bearings differ from^14 -inch in units of .001 inches. The subgroup size isn=5.Subgroup Data Values
1 2.5 .5 2.0 −1.2 1.4
2 .2 .3 .5 1.1 1.5
3 1.5 1.3 1.2 −1.0 .7
4.2.5−2.0 .0 −1.3
5 −.2 .1 .3 −.6 .5
6 1.1 −.5 .6 .5 .2
7 1.1 −1.0 −1.2 1.3 .1
8.2−1.5 −.5 1.5 .3
9 −2.0 −1.5 1.6 1.4 .1
10 −.5 3.2 −.1 −1.0 −1.5
11 .1 1.5 −.2 .3 2.1
12 .0 −2.0 −.5 .6 −.5
13 −1.0 −.5 −.5 −1.0 .2
14 .5 1.3 −1.2 −.5 −2.7
15 1.1 .8 1.5 −1.5 1.2(a) Set up trial control limits forX- andS-control charts.
(b) Does the process appear to have been in control throughout the sampling?
(c) If the answer to part (b) is no, construct revised control limits.
11.Samples ofn = 6 items are taken from a manufacturing process at regular
intervals. A normally distributed quality characteristic is measured, andX and
Svalues are calculated for each sample. After 50 subgroups have been analyzed, we
have∑^50i= 1Xi=970 and∑^50i= 1Si= 85(a) Compute the control limit for theX- andS-control charts. Assume that all
points on both charts plot within the control limits.
(b) If the specification limits are 19±4.0, what are your conclusions regarding
the ability of the process to produce items conforming to specifications?
12.The following data present the number of defective bearing and seal assemblies in
samples of size 100.